Returns for less than one year are not annualized.*Inception date for Class A Shares 9/28/1984.

Returns for less than one year are not annualized.*Inception date for Class C Shares 9/1/1994.

Returns for less than one year are not annualized.*Inception date for Class I Shares 7/5/1996.

Performance data shown represents past performance and is no guarantee of future results. Investment return and principal value will fluctuate so shares, when redeemed, may be worth more or less than their original cost. Current performance may be lower or higher than quoted.

The maximum sales charge for the Fund's A shares is 1.50%.

C shares include a 0.50% contingent deferred sales charge (CDSC) for the first year only.

There is no up-front sales charge for the I shares.

There is no up-front sales charge for class R shares.

FUND OPERATING EXPENSES — Class A Shares

Actual Annual Operating Expenses (fiscal year to date, as of 12/31/2017)

0.73%

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Expense Ratios – Expressed as a percentage of total fund assets and include management fees and operating costs. Expense ratios fluctuate over time and the expense ratio in the prospectus may differ from the actual expense ratio. The fund's total return includes the deduction of expenses.

For more detailed information on fund expenses, please see the fund's prospectus.

FUND OPERATING EXPENSES — Class C Shares

Actual Annual Operating Expenses (fiscal year to date, as of 12/31/2017)

0.97%

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Expense Ratios – Expressed as a percentage of total fund assets and include management fees and operating costs. Expense ratios fluctuate over time and the expense ratio in the prospectus may differ from the actual expense ratio. The fund's total return includes the deduction of expenses.

For more detailed information on fund expenses, please see the fund's prospectus.

FUND OPERATING EXPENSES — Class I Shares

Actual Annual Operating Expenses (fiscal year to date, as of 12/31/2017)

0.41%

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Expense Ratios – Expressed as a percentage of total fund assets and include management fees and operating costs. Expense ratios fluctuate over time and the expense ratio in the prospectus may differ from the actual expense ratio. The fund's total return includes the deduction of expenses.

For more detailed information on fund expenses, please see the fund's prospectus.

MORNINGSTAR RATING™

Overall Morningstar Rating among 173 Muni National Short funds, based on risk-adjusted returns for class A shares, using a weighted average of the fund's three-, five- and ten-year ratings: respectively, 4 stars, 4 stars and 4 stars among 173, 152 and 95 funds, as of 2/28/2018.

MORNINGSTAR RATING™

Overall Morningstar Rating among 173 Muni National Short funds, based on risk-adjusted returns for class C shares, using a weighted average of the fund's three-, five- and ten-year ratings: respectively, 3 stars, 3 stars and 4 stars among 173, 152 and 95 funds, as of 2/28/2018.

MORNINGSTAR RATING™

Overall Morningstar Rating among 173 Muni National Short funds, based on risk-adjusted returns for class I shares, using a weighted average of the fund's three-, five- and ten-year ratings: respectively, 4 stars, 4 stars and 5 stars among 173, 152 and 95 funds, as of 2/28/2018.

LIPPER LEADER as of 12/31/2017 — Class A Shares

The Fund rated a 4 for the three-year period and a 5 for the five- and ten-year periods for Preservation among 5789, 4913 and 3204 funds, respectively.

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Additional Rating and Ranking Information

Lipper ratings for Preservation reflect the funds’ historical loss avoidance relative to other funds within the fixed income asset class. The ratings are subject to change every month and are based on an equal-weighted average of percentile ranks for each metric over three-, five-, and ten-year periods (if applicable). The highest 20% of funds in each peer group are named Lipper Leader, or a score of 5, the next 20% receive a score of 4, the middle 20% are scored 3, the next 20% are scored 2, and the lowest 20% are scored 1. Lipper ratings are not intended to predict future results, and Lipper does not guarantee the accuracy of this information. More information is available at www.lipperweb.com. Thomson Reuters Copyright 2018, All Rights Reserved.

LIPPER LEADER as of 12/31/2017 — Class I Shares

Total Return among 65 funds

Preservation among 5789 funds

In the Short-Intermediate Muni Debt category

The Fund rated a 4 for the three- and five-year periods and a 5 for the ten-year period for Total Return among 65, 61 and 40 funds, respectively.The Fund rated a 4 for the three-year period and a 5 for the five- and ten-year periods for Preservation among 5789, 4913 and 3204 funds, respectively.

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Additional Rating and Ranking Information

Lipper ratings for Total Return reflect funds’ historical total return performance (before sales charge) relative to peers. Lipper ratings for Preservation reflect the funds’ historical loss avoidance relative to other funds within the fixed income asset class. The ratings are subject to change every month and are based on an equal-weighted average of percentile ranks for each metric over three-, five-, and ten-year periods (if applicable). The highest 20% of funds in each peer group are named Lipper Leader, or a score of 5, the next 20% receive a score of 4, the middle 20% are scored 3, the next 20% are scored 2, and the lowest 20% are scored 1. Lipper ratings are not intended to predict future results, and Lipper does not guarantee the accuracy of this information. More information is available at www.lipperweb.com. Thomson Reuters Copyright 2018, All Rights Reserved.

30-Day Yields With Sales Charge as of 2/28/2018 — Class A Shares

Annualized Distribution Yield

1.88%

SEC Yield

1.23%

30-Day Yields as of 2/28/2018 — Class C Shares

Annualized Distribution Yield

1.67%

SEC Yield

1.01%

30-Day Yields as of 2/28/2018 — Class I Shares

Annualized Distribution Yield

2.16%

SEC Yield

1.50%

Dividends and Capital Gains — Class A Shares

Dividend (paid Feb 28, 2018)

$0.02137

Capital Gains (2017)

None Paid

Dividends and Capital Gains — Class C Shares

Dividend (paid Feb 28, 2018)

$0.01880

Capital Gains (2017)

None Paid

Dividends and Capital Gains — Class I Shares

Dividend (paid Feb 28, 2018)

$0.02413

Capital Gains (2017)

None Paid

Net Asset Value (NAV) History as of 2/28/2018 — Class A Shares

Net Asset Value (NAV) History as of 2/28/2018 — Class C Shares

Net Asset Value (NAV) History as of 2/28/2018 — Class I Shares

2018 has already seen several events impacting the municipal bond market. Whether it is tax reform, infrastructure spending, or interest rate increases from the Federal Reserve, the potential effects on investor’s portfolios could be dramatic.

Best Short-Intermediate Municipal Debt Fund - Eight Years in a Row

2018 – Class I shares for the 10-year period ended 11/30/17,
among 39 funds.

2017 – Class I shares for the 10-year period ended 11/30/16,
among 41 funds.

2016 – Class I shares for the 10-year period ended 11/30/15,
among 39 funds.

2015 – Class I shares for the 10-year period ended 11/30/14,
among 33 funds.

2014 – Class I shares for the 10-year period ended 11/30/13,
among 29 funds.

2013 – Class I shares for the 5- and 10-year periods ended 11/30/12,
among 31 and 25 funds.

2012 – Class I shares for the 5- and 10-year periods ended 11/30/11,
among 30 and 23 funds.

Lipper Fund Awards are granted annually to the
fund in each Lipper classification that
consistently delivered the strongest risk-adjusted
performance (calculated with dividends
reinvested and without sales charge).
Fund Classification Awards are given for three-year,
five-year, and ten-year periods. Thornburg did not win the award for any other time period. Past performance
does not guarantee future results.

Important InformationBefore investing, carefully consider the Fund’s investment goals, risks, charges, and expenses. For a prospectus or summary prospectus containing this and other information, contact your financial advisor or visit our literature center. Read them carefully before investing.

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Investments carry risks, including possible loss of principal. Portfolios investing in bonds have the same interest rate, inflation, and credit risks that are associated with the underlying bonds. The value of bonds will fluctuate relative to changes in interest rates, decreasing when interest rates rise. Unlike bonds, bond funds have ongoing fees and expenses. Investments in the Fund are not FDIC insured, nor are they bank deposits or guaranteed by a bank or any other entity.

Credit quality ratings for Thornburg’s municipal portfolios used the highest rating available from either S&P Global Ratings or Moody’s Investors Service.

A bond credit rating assesses the financial ability of a debt issuer to make timely payments of principal and interest. Ratings of AAA (the highest), AA, A, and BBB are investment-grade quality. Ratings of BB, B, CCC, CC, C and D (the lowest) are considered below investment grade, speculative grade, or junk bonds.

Diversification does not assure or guarantee better performance and cannot eliminate the risk of investment losses.

Income earned from municipal bonds is exempt from regular federal and in some cases, state and local income tax. Income may be subject to the alternative minimum tax (AMT).

The laddering strategy does not assure or guarantee better performance than a non-laddered portfolio and cannot eliminate the risk of investment losses.

Class I shares may not be available to all investors. Minimum investments for the I share class may be higher than those for other classes.

There is no guarantee that the Fund will meet its investment objectives.

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Important Disclosure: For Professional Investors Only

This area of our web site is only directed at non-U.S., institutional and professional investors and is not suitable for individual investors.

The information regarding funds for non-U.S. investors is for informational purposes only, does not constitute an offer for shares, products or services and should not be construed as an offer to sell or a solicitation of an offer to buy to any persons who are prohibited from receiving such information under the laws applicable to their place of citizenship, domicile or residence.

This site is operated by Thornburg Investment Management, Inc. on behalf of Thornburg Investment Management Ltd. and Thornburg Global Investment plc. Before continuing, please read the following important information and if you continue on, you confirm that you have read and agree to these provisions. Thornburg Global Investment plc is authorised under the UCITS Regulations and provides shares in UCITS registered Funds for non-U.S. investors. The Funds of the Company are registered in Ireland and are available only to residents of those jurisdictions where allowed by applicable law. Purchase orders from U.S. persons or other ineligible investors will not be accepted by the Fund’s Administrator.

Thornburg Investment Management Ltd. is an Appointed Representative of Robert Quinn Advisory LLP, which is authorised and regulated by the Financial Conduct Authority in the United Kingdom (no. 548030). Thornburg Investment Management Ltd. manages Thornburg's international business development and relationship management activities. Registered in England and Wales no. OC385286.

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